The invention relates to a process for forming simvastatin or simvastatin precursors using improved LovD acyltransferase mediated acylations.
Enzymes are biomolecules which catalyze the conversion of a chemical substrate into a product and have been used in the chemical synthesis of valuable natural products and pharmaceuticals. Advantageously, enzymes can function to increase the rate of chemical conversion of a substrate to a product (by lowering the activation energy for the reaction) and to direct the placement of functional groups, i.e. regioselectively and/or stereoselectively placing functional groups onto a substrate. Enzyme activity can be affected by other molecules known as inhibitors. These inhibitors function to decrease enzyme activity and can severely limit the conversion or rate of conversion of a starting substrate into product.
One particular group of useful enzymes includes the transferases. Transferases are enzymes that catalyze the transfer of a functional group, for example, alkyl, acyl or phosphate groups, from a substrate (designated the donor and sometimes known as the coenzyme) to another substrate (designated the acceptor). The enzyme thereby catalyzes a reaction between chemical compounds that results in the loss of functionality from the donor and a gain in functionality on the acceptor. The subclass of acyltransferases has been used, among other things, to regioselectively acylate chemical substrates such as monacolin J to form simvastatin.
Simvastatin is a semisynthetic derivative of the natural product lovastatin, which can be isolated from the fermentation broth of Aspergillus terreus. Both lovastatin and simvastatin are cholesterol lowering drugs that substantially lower the risk of heart disease among adults. The gene cluster for lovastatin biosynthesis in A. terreus has been described previously, for example, in U.S. Pat. No. 6,391,583. Encoded in the gene cluster is a 46 kD protein known as LovD, which functions as an acyltransferase.
Once lovastatin is produced via fermentation in an A. terreus host, simvastatin can be produced from lovastatin via a semisynthetic route. After isolation and purification of lovastatin from the fermentation broth, a typical semisynthesis can proceed by hydrolysis of the 2-methylbutyrate side arm in the presence of base to yield the intermediate monacolin J. Monacolin J is the immediate precursor to simvastatin. Following hydrolysis, the free acid is lactonized, the free hydroxyl at C13 is protected, and the C8 alcohol is acylated to provide a protected analogue of simvastatin. Subsequent deprotection affords simvastatin. See, e.g., WO 2007/139871.
Enzymatic transformations using lipases and esterases have also been investigated as alternatives to chemical derivation. See, e.g., PCT WO 2005/040107, PCT WO 94/26920 and T. G. Schimmel, et. al. in Appl. Environ. Microbiol. (1997) 63:1307-1311. Enzymatic variants suffer from decreased throughput of substrate, high loading requirements, slow enzyme conversion rate or poor enzyme turnover. Therefore, an enzymatic method of producing simvastatin, such as by selective acylation of the C8 hydroxy of monacolin J, which provides good to high yield with minimum isolation steps, good enzyme turnover and conversion rate, and/or reasonable loading requirements is important towards the efficient synthesis of simvastatin and additional statin analogs.
Accordingly, there has been a long-felt need for an enzymatic process which overcomes one or more limitations of the prior art, thereby providing a method for the efficient and expedient acylation of chemical substrates such as lovastatin or monacolin J using acyltransferases.